Split lock screw fastener assembly and method

ABSTRACT

A self-locking bolt assembly ( 1 ) includes a split bolt ( 2 ) and a screw set pin ( 3 ). The bolt includes a threaded shank ( 4 ), an axial bore ( 6 ) extending through the shank, the bore ( 6 ) including a threaded bore section ( 6 A), a tapered end section ( 6 C), and a bore midsection ( 6 B) between the threaded bore section and the tapered end section. The screw set pin( 3 ) includes a screw section ( 10 B) having threads for engaging the threaded bore section ( 6 A) and a pin shaft ( 10 ) having a tapered end section ( 10 A) for engaging the tapered end section ( 6 C) of the bore ( 6 ), the pin shaft ( 10 ) having a proximal end attached to the screw section ( 10 B). The pin shaft ( 10 ) is sufficiently long to ensure that the screw set pin ( 3 ) further into the bore ( 6 ) without galling threads of the screw section ( 10 B). The tapered end section ( 10 A) of the pin shaft has a taper angle (α) that is less than a taper angle (β) of the tapered end section ( 6 C) of the bore ( 6 ) to allow a narrowed end portion of the tapered end section ( 10 A) of the pin shaft ( 10 ) to engage a narrowed end portion of the tapered end section ( 6 C) of the bore ( 6 ).

[0001] This application claims the benefit of prior filed co-pendingU.S. provisional application Serial. No. 60/412,358 filed Sep. 21, 2002entitled “SPLIT LOCK SCREW FASTENER ASSEMBLY” by Patrick William Breslinand Mary Ann Breslin.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to a screw lockingassembly including a hollow split stud or split bolt and a screw set-pinthat is tightened into the hollow split bolt to lock it tightly into ahole or threaded hole in a medial body. More particularly, the presentinvention relates to improvements that greatly increase the mechanicaladvantage between torque applied to the pin setscrew and expansion of asplit distal end portion of the bolt and to preventing loosening of thepin setscrew with respect to the split bolt and to preventing looseningof the split bolt with respect to the bolt-receiving hole withoutgalling and causing injury to the threads of either the bolt bore or thepin setscrew as in the prior art.

[0003] The closest prior art is believed to include U.S. Pat. No.322,657 entitled “Screw Bolt Lock” issued to Tolman on Jul. 21, 1885,U.S. Pat. No. 2,463,859 entitled “Threaded Locking Device” issued Jul.25, 1945 to Engstrom, and U.S. Pat. No. 2,479,075 entitled “ScrewLocking Means” issued to Martin on Nov. 24, 1944.

[0004] U.S. Pat. No. 322,657 discloses a screw bolt lock including ascrew bolt A with a threaded central aperture C having a tapered sectionE and accommodating a screw or center pin F that spreads a slitted endsection D of the bolt apart to lock the bolt into a threaded hole. Asshown in FIG. 1 of U.S. Pat. No. 322,657, the center pin F is threadedup to the tapered section E of the bolt bore. The bolt bore is threadedto the point at which the distal end of the bore becomes tapered.

[0005] Similarly, U.S. Pat. No. 2,479,075 discloses a device in which ascrew 11 having a bore 14 with slits 13 accepts a threaded plug 21having a conical end taper 19 conforming to a tapered end section 17 ofthe bore. The tightening of the threaded plug is described as causingthe conical end taper of the threaded plug to engage the tapered boresection 17, thereby expanding the slitted end of the screw 11 andlocking it into a threaded hole of a body. U.S. Pat. No. 2,463,859discloses another similar device in which a bolt has a partiallythreaded bore 4 that extends from the head of the bolt to a distal endportion thereof. Slits 8 are formed in the distal end portion of thebolt. A threaded expander stud 9 is threaded into bolt bore 4 to the endof the threaded portion. Further tightening of the stud causes it toengage a reduced diameter distal portion of the bore 4, causingexpansion of the slitted distal end of the bolt, thereby locking theslitted distal end into a threaded hole.

[0006] The devices disclosed in the above described references have theshortcoming that the pin setscrews disclosed in the above references“bottom out” or “heel” on the lead-in threads of the bolt bore beforethe tapered distal end section of the pin setscrew reaches the taperedsection of the bolt bore. The tapered distal end of the pin setscrewnever comes in contact with the tapered section of the inner bore of thebolt because of the commonly known lead-in threads, required on alltapped blind holes, which bind the pin in the lead-in threads before itcan reach the tapered section of the inner bore of the bolt. Tighteningof the center pin, referred to herein as the “pin setscrew”, in order toadvance its distal threaded section sufficiently further into theunthreaded section of the bolt bore to spread the distal end of the boltwould cause the threads of the pin setscrew to gall on the threads ofthe bolt and cause strain and injury to the threads of both the pinsetscrew and the bolt such that neither would be reusable, as recognizedin the Tolman patent. (The term “galling” refers to a severe form ofadhesive way or that occurs during sliding contact of one surfacerelative to another, wherein clumps of one part may break away from onesurface and stick to the other surface.) Such galling would necessitatethat an extremely large amount of torque be applied to the pin setscrewto advance it into the reduced-diameter portion of the bolt bore. Also,there would be inadequate mechanical advantage of torque applied betweenthe bolt end of the pin setscrew to advance the pin setscrew so as todevelop sufficient outward force on the split distal end sections of thebolt to expand them and adequately lock the bolt into the bolt-receivinghole. It would not be practical for the user to apply enough force tothe pin setscrew to spread the distal split end of the bolt enough tocause an adequate locking effect, and the force would not be equallyapplied to all fingers to spread the bolt because of the diminishingroot depth of the lead in threads of the bolt bore screw section as thepin setscrew is turned. Furthermore, the prior art does not provide anyway of locking the pin setscrew to the bolt into when it is screwed intothe bolt.

[0007] Despite the efforts in the prior art, there has been a very longand unfulfilled need for a practical, highly reliable self-locking bolt.For more than 200 years there has been a need for a locking fastenerthat is simple to use without use of parts that need to be assembledwhile installing and locking the fastener. An example of an applicationin which there has been a very long felt need for a reliableself-locking bolt is in the field of high-performance internalcombustion engines, wherein exhaust manifold bolts frequently becomeloosened due to vibration and thermal cycling. No really reliablesolution to this problem has ever been provided. There also are numerousother examples in which there has been a long felt need for a reliableself-locking bolt, including engine oil pump mounting applications,industrial press brake tool attachment applications, mining wheel andhub attachment applications, railroad track attachment applications, andmany more.

[0008] There also is an unmet need for a simple true locking fastenerthat surpasses the IFI-124 and MIL-DTL-18240F specifications wherein thebolt and pin assembly securely locks, does not unlock under vibration orheat stress, and is not torque-dependent.

SUMMARY OF THE INVENTION

[0009] It is an object of the invention to provide a locking split boltand screw set pin assembly that avoids galling of threads of the screwset pin into threads of a bore extending through the split bolt withoutstrain and injury to the threads of either the bolt or screw set pin.

[0010] It is another object of the invention to provide a locking splitbolt and screw set pin assembly that provides minimum frictionalresistance to tightening of the screw set pin into a bore extendingthrough the split bolt.

[0011] It is another object of the invention to provide a locking splitbolt and screw set pin assembly that provides maximum mechanicaladvantage for tightening of the screw set pin into a bore extendingthrough the split bolt to expand a threaded split distal portion of thebolt against threads of a receiving hole into which the bolt has beentightened and to lock the threads of the split bolt into place in thereceiving hole.

[0012] It is another object of the invention to provide a locking splitbolt and screw set pin assembly that provides maximum mechanicaladvantage for tightening of the screw set pin into a bore extendingthrough the split bolt to expand a threaded split distal end portion ofthe bolt against threads of a receiving hole into which the bolt hasbeen tightened to lock the bolt and screw set pin into place in thereceiving hole and that also prevents loosening of the bolt and screwset pin due to various conditions, such as mechanical vibration and/orthermal cycling of a body in which the receiving hole is formed.

[0013] It is another object of the invention to provide a true lockingfastener that meets or surpasses the IFI-124 and MIL-DTL-18240Fspecifications.

[0014] It is another object of the invention to provide a true lockingscrew set pin in a locking fastener including a hollow split stud orbolt.

[0015] It is another object of the invention to provide a lockingfastener including a hollow split bolt and a screw set pin which can bereusable.

[0016] It is another object of invention to provide a true lockingfastener that is easy to install without use of complicating componentsor accessories.

[0017] It is another object of invention to provide a true lockingfastener that is in completely assembled form prior to use as a lockingfastener.

[0018] It is another object of invention to provide a locking fastenerincluding a split bolt wherein the degree of locking is not dependent onthe amount of torque applied to the split bolt.

[0019] It is another object of the invention to provide a mechanicallocking fastener with an internal locking mechanism.

[0020] It is another object of the invention to provide a lockingfastener including a split bolt wherein the split bolt has maximumtensile strength.

[0021] It is another object of the invention to provide a lockingfastener including a split bolt wherein an internal locking mechanismspreads split finger portions of the bolt symmetrically.

[0022] Briefly described, and in accordance with one embodiment, thepresent invention provides a self-locking bolt assembly (1) including abolt (2) including a threaded shank (4), an axial bore (6) extendingthrough the shank, the bore (6) including a threaded bore section (6A),a tapered end section (6C), and a bore midsection (6B) between thethreaded bore section and the tapered end section and a screw set pin(3) including a screw section (10B) having threads for engaging thethreaded bore section (6A) and a pin shaft (10) having a tapered endsection (10A) for engaging the tapered end section (6C) of the bore (6),the pin shaft (10) having a proximal end attached to the screw section(10B). The pin shaft (10) is sufficiently long to ensure that when thetapered distal end section (10A) engages the tapered end section (6C) ofthe bore the screw set pin (3) then can be screwed a predetermineddistance further into the bore (6) without galling threads of the screwsection (10B) and threaded bore section (6A). The tapered end section(10A) of the pin shaft (10) has a taper angle (α) that is less than ataper angle (β) of the tapered end section (6C) of the bore (6) to allowa narrowed end portion of the tapered end section (10A) of the pin shaft(10) to engage a narrowed end portion of the tapered end section (6C) ofthe bore (6).

[0023] In the described embodiments, a plurality of slits (7) extendthrough a distal end section (20) of the shank (4) that includes thetapered end section (6C) of the bore (6). The pin shaft (10) has adiameter that is less than a diameter of the threaded bore section(6A)to allow the pin shaft (10) to pass through the threaded bore sectionwithout engaging threads thereof. The self-locking bolt assembly ofclaim 1 is screwed into a body (15) having a threaded bolt-receivinghole (15A) therein, with the screw set pin (3) tightened sufficientlyinto the bolt (2) to cause the tapered end section (10A) of the pinshaft (10) to expand a distal end section (20) of the shank (4) enoughthat threads (4A) of the shank tightly engage threads of thebolt-receiving hole (15A) and become locked into the body (15). Thescrew set pin (3) is also tightened sufficiently into the bolt (2) tocause the tapered end section (10A) of the pin shaft (10) tosufficiently symmetrically expand bolt fingers defined by the slits thatcentral contact areas (C) of the fingers elastically deform and dig intothe bolt-receiving hole (15A) enough to securely lock the bolt (2) tothe body (15). The bore of the bolt is provided in such away as tocreate a differential in the radius of the internal tapered borecompared to the radius of the tapered end of the screw set pin, wherethe differential in the radius creates localized high-pressure points ofcontact between the internal tapered bore and the tapered end of thescrew set pin without requiring a great deal of torque on the screw setpin to effectively lock it relative to the bolt and in order toeffectively lock the bolt into a bolt-receiving hole.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is an exploded, partial cutaway side elevation view of ahollow split bolt and screw set pin assembly of the present invention.

[0025]FIG. 2 is a left elevation view of the split bolt portion of theassembly shown in FIG. 1.

[0026]FIG. 3 is a left elevation view of the assembly shown in FIG. 1with the screw set pin in the bore of the split bolt.

[0027]FIG. 4 is a section view of the assembly of FIG. 1 with the splitbolt threaded into a receiving hole and the screw set pin threaded intothe bore of the split bolt.

[0028]FIG. 5 is an enlarged view of the right portion of FIG. 4 markedto facilitate explanation of the operation of the split bolt and screwset pin assembly.

[0029]FIG. 6 is a diagram of the assembly as shown in the section viewof FIG. 4 with the screw set pin sufficiently tightened to expand thesplit distal end portion of the split bolt.

[0030]FIG. 7 is a diagram of the assembly as shown in FIG. 6 with theshank 4 of the split bolt 2 threaded into a body 15.

[0031]FIGS. 8A and 8B are partial section view diagrams that are usefulin explaining the mechanism involved in the self-locking properties ofthe split bolt and screw set pin assembly of the present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Referring to FIGS. 1-3, a split bolt and screw set pin assembly 1includes a hollow split bolt 2 having an axial bolt bore indicated byhidden dashed line 6 and a screw set pin 3 which can be inserted intoand tightened into bolt bore 6. Split bolt 2 includes an ordinary bolthead 5 having facets 5A for engagement by a wrench or the like, and alsoincludes a threaded shank 4 through which bolt bore 6 extends. (Anannular clamping flange 17 as shown in FIG. 4 can be included as part ofbolt head 5.) Shank 4 includes conventional threads 4A on itscylindrical outer surface. A distal end portion 20 of split bolt 2includes one or more slits 7 to allow expansion of the distal endportion 20 by screw set pin 3, as subsequently explained. Typically,there may be 4 to 8 slits, depending on the size of the fastener.

[0033] Bolt bore 6 includes, from left to right, a proximal cylindricalthreaded section 6A having internal threads 12, a cylindricalreduced-diameter midsection 6B continuous with threaded section 6A, aconically tapered section 6C continuous with mid-section 6B, and adistal further-reduced-diameter end section 6D that is formed by theslits 7 and is continuous with tapered section 6C and extends to the endof shank 4.

[0034] By way of definition, the term “bolt” as used herein includes athreaded shaft and an ordinary bolt head or any other feature attachedto bore included in the shaft that enables work to be applied to theshaft to advance it or thread it into a threaded bolt-receiving hole.Note that the self-locking feature of the invention can be provided fora self-tapping bolt or screw, and also can be provided for a wide rangeof sizes of bolts, studs, and screws.

[0035] Screw set pin 3, includes an elongated cylindrical pin section 10which fits easily into midsection 6B of bolt bore 6 and a conicallytapered distal end section 10A having a “shallower” taper angle than thetaper angle of bolt bore section 6C. Pin section 10 of screw set pin 3may have a minimum suitable diameter, which allows use of a minimumdiameter of the bore mid-section 6B in order to provide maximum strengthof bolt shank 4. A section 10B of screw set pin 3 is attached to theproximal end of pin section 10, and in the embodiment shown in FIG. 1,includes a hex key opening 11 for receiving a hex key with which totighten screw set pin 3 into bolt bore 6. Of course, various other ways,such as providing a specialized head or handle, could be provided forengaging section 10B to tighten it using tools other than a hex wrench.Similarly, the head of split bolt 2 can be adapted to have a handle, andscrew set pin 3 also can be adapted to have a handle. Split bolt 2 canbe composed of the various materials of which ordinary bolts, screws,and studs are commonly composed for various applications, and screw setpin 3 also can be composed of the same materials of which ordinary setscrews are commonly composed for various applications.

[0036] By way of definition, the head of split bolt 2 can be adapted toinclude features, such as one or more annular flanges, to engage or“capture” any type of auxiliary member (not shown) that is spaced fromthe body 15 into which the distal section 20 of shank 4 is threaded, andscrew set pin 3 can be loosened to allow split bolt 2 to be suitablyadjusted relative to body 2 so as to support the auxiliary member at anysuitable distance from body 2.

[0037] Referring to FIGS. 4-6, split bolt 2 is threaded into a receivinghole 15A of a body 15 and screw set pin 3 is inserted into the proximalend portion 6A of bolt bore 6. When section 10B of screw set pin 3 istightened enough that tapered section 10A of pin section 10 abuts thedifferently tapered section 6C of bolt bore 6 at a contact area 26 (thatinitially is generally annular), as shown in FIG. 4, the contact area 26is positioned at the point indicated by dashed line 31 in FIG. 5. Inthis configuration as shown in FIG. 4, when the right end of taperedsection 10A of screw set pin 3 first touches contact area 26 of taperedsection 6C of bolt bore 6, the threads 12 in section 6A of bolt bore 6extend substantially further to the right than the threads of section10B. Consequently, the threads of section 10B do not ever gall into theunthreaded material of split bolt 2, as occurs in the previouslydescribed prior art.

[0038] Further tightening of screw set pin 3 forces tapered section 10Aof screw set pin 3 further against and into tapered distal section 6C ofbolt bore 6, thereby forcing expansion of the inner and outer diametersurfaces of the distal section 20 of split bolt 2, thereby wedging thebolt into and locking it into the threaded hole of the medial body 15.(The initially annular contact area 26 “evolves” into eight much smallercontact areas 26 as tapered section 10A of screw set pin 3 forcesexpansion of the slitted fingers 20D-1,2,3,4 of split bolt 2, assubsequently explained with reference to FIGS. 8A and 8B.)

[0039] It should be noted that the threads of the screw set pin shouldbe as short as possible to keep the surface area of threaded contact toa minimum and reduce friction between the threads 10B of screw set pin 3and the threads of a section 6A of bolt bore 6.

[0040] Unlocking of the split-lock bolt is very simple and reliable, asscrew set pin 3 is simply un-tightened. That automatically loosens splitbolt 2, and then it is easily adjusted within bolt-receiving hole 15Aand can be re-tightened or removed from bolt-receiving hole 15A.

[0041] As shown in FIGS. 2, 4 and 5, the taper angle α of taperedsection 10A screw set pin 3 is less than the taper angle β of taperedsection 6C of bolt bore 6. The incline or taper angle α of the taperedsection 10A of screw set pin 3 being less than the incline or taperangle β of tapered section 6C of bolt bore 6 prevents screw set pin 3from “bottoming” or “heeling” on tapered section 6C bore 6, and insteadcauses the extreme end of tapered section 10A to apply a workforce tothe most distal or distant portions of tapered section 6C. Thus, thedistance 32 between contact area 26 and the beginning location 21 ofslit 7 is significantly greater than would be the case if the two taperangles α and β were equal. The increased distance 32 between thelocation 21 about which the fingers 20D-1,2,3,4 (FIG. 2) bend or “pivot”and the location of the contact area 26 increases the mechanicaladvantage for expanding fingers 20D-1,2,3,4 outwardly as screw set pin 3is further tightened into bolt bore 6. The greater mechanical advantageis achieved in expanding the four fingers 20D-1,2,3,4 of split distalportion 20 of split bolt 2 by tightening screw set pin 3 because thedescribed configuration provides the greatest distance 32 from thelocation 21 of the beginning of the slits 7 and the location 31 at whichoutward forces are applied to expand fingers 20D-1,2,3,4.

[0042] The incline angle α of tapered section 10A of screw set pin 3being less than incline angle β of the tapered section 6C of bolt bore 6also provides a minimal amount of contact area 26 between screw set pin3 and split bolt 2. This results in minimum surface friction betweenscrew set pin 3 and split bolt 2 as screw set pin 3 is tightened intosplit bolt 2. The outward forces of fingers 20D-1,2,3,4 on the threadsof bolt-receiving hole 15A act so as to lock split bolt 2 tightly intobolt-receiving hole 15A. The details of the locking mechanics of thescrew set pin involved are subsequently explained with reference toFIGS. 8A and 8B. The inwardly directed forces of fingers 20D-1,2,3,4 onthe reduced contact areas 26 between tapered sections 10A and 6C act soas to lock the tightened screw set pin 3 in place and prevent it frombecoming loosened during mechanical vibration and/or thermal cycling ofbody 15 into which split bolt is threaded.

[0043] The above described locking split bolt/screw set pin assemblyprovides maximum outward pressure of the fingers of slotted distalportion of the split bolt which is relatively uniformly applied againstthe receiving hole 15A of the body 15 into which split bolt 2 issecurely locked. Also, the contact area 26 between screw set pin 3 andfingers 20D-1,2,3,4 is reduced, and therefore causes high-pressurepoints to lock screw set pin 3 into place, as subsequently explained inmore detail.

[0044]FIG. 6 shows screw set pin 3 sufficiently tightened into splitbolt 2 to expand the split distal end portion of the split bolt. Theoutward radial component of force applied by tapered section 10A at thecontact area 26 (FIG. 5) to tapered section 6C of bolt bore 6 causes thefingers of section 20 to expand outward as shown. In FIG. 6, arcs 34,36, 38 and 40 are provided to show that the further screw set pin 3 isadvanced into section 6C of bore 6, the greater the differential isbetween the two radii that determine the amount of contact area 26, andtherefore the greater the reduction is in the amount of contact area 26,and therefore the greater the pressure is that increases the extent towhich screw set pin 3 is locked into place.

[0045]FIG. 7 shows expansion of the distal portion 20 of split bolt 2 asin FIG. 6, but with the shank 4 of the split bolt 2 threaded intobolt-receiving hole 15A of body 15, wherein the expanded threads ofdistal section 20 of split bolt 2 “fill up” the threads ofbolt-receiving hole 15A much more tightly than is the case for theremaining threads 14A of split bolt 2.

[0046] Referring to FIGS. 8A and 8B, note that the radius of curvatureof the inner surfaces of fingers 20D-1,2,3,4 does not increase as thefingers are forced to expand outwardly. That is, the split fingers20D-1,2,3,4 retain their original radii of curvature as they areexpanded outward by the outward force of tapered distal end section 10Aof screw set pin 3 upon tapered section 6C of bolt bore 6. In FIG. 8A, asection view is shown at the location at which a portion 10A-1 oftapered distal end section 10A of screw set pin 3 just uniformly touchesthe tapered section 6C of bolt bore 6, so the contact area 26 initiallyis generally annular. For simplicity, only finger 20D-1 is shown, andthe uniform contact area between tapered distal end section 10A andfinger 20D-1 is indicated by reference numeral 26 in FIG. 8A.

[0047] In FIG. 8B, another section view is shown after screw set pin 3has been tightened so that its tapered distal end section 10A hasexpanded fingers 20D-1,2,3,4 so that the outer threads thereof areforced tightly into the inner threads of bolt-receiving hole 15A. Notethat the radius of curvature of the threads of bolt-receiving hole 15Ain body 15 is necessarily greater than the radii of curvature of theouter threads of the outwardly expanded finger 20D-1. Consequently, thecontact area C between the inner threads of bolt-receiving hole 15A andthe outer threads of finger 20D-1 is confined to the central area of theouter threads of finger 20D-1. This causes the contact area of the outerthreads of finger 20D-1 to tend to dig into and elastically deform thethreads 15B of body 15 in the contact area C. This causes the distalportion 20 of split bolt 2 to be very securely locked with respect tobody 15.

[0048]FIG. 8B also shows that larger radius portion 10A-2 of tapereddistal end section 10A contacts the inner surfaces of finger 20D-1,which has the same small radius of curvature as in FIG. 8A, whichcreates the small contact areas at points A and B, which representportions of the reduced contact area 26. This causes the two contactareas of the endpoints of finger 20D-1 to tend to dig into, grip, andelastically deform the surface of tapered distal end section 10A ofscrew set pin 3 at the locations of the two contact areas A and B. Thiscauses screw set pin 3 to be locked very securely with respect to splitbolt 2.

[0049] An advantage of split bolt and screw set pin assembly 1 is thatshank 4 of split-lock bolt 2 can be as long or large in diameter asdesired for various applications, and can be easily locked at anyselected depth in a threaded hole of a receiving object, by simplytightening the screw set pin. The selected depth can be easilyreadjusted at any time by simply loosening the screw set pin and turningthe outer bolt to the desired depth and re-tightening the screw set pin.

[0050] Another important advantage of the above described split bolt andscrew set pin assembly 1 in some applications is that the pressure orforce of the bolt head or clamping flange of the split bolt upon amember being fastened to the receiving object is completely independentof how tightly the split-lock bolt is locked to the receiving object.Thus, a small clamping force may be provided on a soft or fragile memberby the split-lock bolt, yet the split bolt 2 may be locked extremelytightly to the body 15.

[0051] It should be understood that the expansion of the locking threads4A of split bolt 2 into the receiving threads 15B of receiving hole 15Aeffectively “fills up” the groove between the threads 15B of receivinghole 15 as shown in FIG. 7 when distal section 20 of split bolt 2 ismaximally expanded by tightening of screw set pin 3 into split bolt 2.The filling of the groove results in the distal section 20 of split bolt2 being essentially unitary with the body 15 and also results in minimaldiscontinuity in the boundary region between them so as to greatlyreduce microscopic effects of vibration and/or thermal cycling whichotherwise tend to induce loosening of split bolt 2 from threaded hole15A in body 15.

[0052] For example, in high-performance internal combustion engines, theexhaust manifolds have always been bolted to the engine block, but untilnow there has been no good solution to the problem of the boltseventually becoming loosened due to the extreme amount of vibration andthermal cycling to which they are subjected. The present inventors haveproven that the above described split-lock bolt completely solves thisproblem.

[0053] Thus, the above described invention provides a screw set pinextending into the proximal end of a threaded bore extending through asplit bolt having a reduced-diameter slotted distal end portion alongwith a small-diameter screw set pin so as to avoid galling of threads ofthe screw set pin and the bolt bore, and provides an angularrelationship between taper of the distal end of the screw set pin andthe tapered portion of the bolt bore that provides maximum mechanicaladvantage for tightening of the screw set pin to expand the distalslotted portion of the bolt to effectively lock it into the receivinghole, minimizes friction between the screw set pin and the bolt, andalso locks the screw set pin into the bolt bore.

[0054] While the invention has been described with reference to severalparticular embodiments thereof, those skilled in the art will be able tomake various modifications to the described embodiments of the inventionwithout departing from its true spirit and scope. It is intended thatall elements or steps which are insubstantially different from thoserecited in the claims but perform substantially the same functions,respectively, in substantially the same way to achieve the same resultas what is claimed are within the scope of the invention. For example,slits 7 in the distal end section 20 of bolt 2 could be omitted in somecases if the outer bolt is composed of suitable material.

What is claimed is:
 1. A self-locking bolt assembly comprising: (a) abolt including a threaded shank, an axial bore extending through theshank, the bore including a threaded bore section, a tapered endsection, and a bore midsection between the threaded bore section and thetapered end section; (b) a screw set pin including a screw sectionhaving threads for engaging the threaded bore section and a pin shafthaving a tapered end section for engaging the tapered end section of thebore, the pin shaft having a proximal end attached to the screw section,the pin shaft being sufficiently long to ensure that when the tapereddistal end section engages the tapered end section of the bore the screwset pin then can be screwed a predetermined distance further into thebore without galling threads of the screw section and the threaded boresection.
 2. The self-locking bolt assembly of claim 1 wherein thetapered end section of the pin shaft has a taper angle that is less thana taper angle of the tapered end section of the bore to allow a narrowedend portion of the tapered end section of the pin shaft to engage anarrowed end portion of the tapered end section of the bore.
 3. Theself-locking bolt assembly of claim 2 including a plurality of slitsextending through a distal end section of the shank that includes thetapered end section of the bore.
 4. The self-locking bolt assembly ofclaim 3 wherein the plurality of slits includes a pair of diametricallyopposed slits.
 5. The self-locking bolt assembly of claim 1 wherein aproximal end of the screw set pin includes a feature for applying torqueto the screw set pin.
 6. The self-locking bolt assembly of claim 5wherein the torque-applying feature includes a key opening for receivinga torque-applying device.
 7. The self-locking bolt assembly of claim 1wherein the pin shaft has a diameter that is less than a diameter of thethreaded bore section to allow the pin shaft to pass through thethreaded bore section without engaging threads thereof.
 8. Theself-locking bolt assembly of claim 1 wherein the bolt includes a bolthead attached to the shank, and wherein the bore extends through thebolt head.
 9. The self-locking bolt assembly of claim 1 including a bodyhaving a threaded bolt-receiving hole therein, with the screw set pintightened sufficiently into the bolt to cause the tapered end section ofthe pin shaft to expand a distal end section of the shank enough thatthreads of the shank tightly engage threads of the bolt-receiving holeand become locked into the body.
 10. The self-locking bolt assembly ofclaim 3 including a body having a threaded bolt-receiving hole therein,with the screw set pin tightened sufficiently into the bolt to cause thetapered end section of the pin shaft to sufficiently expand fingersdefined by the slits that central contact areas of the fingerselastically deform and dig into the bolt-receiving hole enough tosecurely lock the bolt to the body.
 11. The self-locking bolt assemblyof claim 10 wherein edge contact areas of the fingers deform and diginto the tapered end section of the pin shaft enough to securely lockthe screw set pin to the bolt.
 12. A method of using a self-locking boltassembly including a bolt including a threaded shank having an axialbore extending through the shank for receiving a screw set pin includinga screw section having threads for engaging a threaded bore section ofthe bore, the screw set pin also including a tapered end section, themethod comprising: (a) providing a bore midsection between the threadedbore section and the tapered end section; and (b) providing a pin shafthaving one end attached to the screw section and a tapered end sectionfor engaging the tapered end section of the bore, the pin shaft beingsufficiently long to ensure that when the tapered distal end section ofthe pin shaft engages the tapered end section of the bore the screw setpin then can be tightened a predetermined distance further into the borewithout galling threads of the screw section and the threaded boresection.
 13. The method of claim 12 including screwing the screw set pinsufficiently far into the bolt enough to abut the tapered end section ofthe pin shaft against the tapered end section of the bore, and causingonly a narrowed end portion of the tapered end section of the pin shaftto engage a narrowed end portion of the tapered end section of the boreby providing the tapered end section of the pin shaft with a taper anglethat is less than a taper angle of the tapered end section of the bore.14. The method of claim 12 including providing a plurality of slitsextending through a distal end section of the shank including thetapered end section of the bore.
 15. The method of claim 12 wherein thediameter of the pin shaft has a diameter that is less than a diameter ofthe threaded bore section of the bore, the method including advancingthe pin shaft through the threaded bore section without engaging threadsthereof.
 16. The method of claim 14 including locking the self-lockingbolt assembly into a threaded bolt-receiving hole in a body bytightening the screw set pin sufficiently far into the bolt to cause thetapered end section of the pin shaft to sufficiently expand fingersdefined by the slits that central contact areas of the fingerselastically deform and dig into the bolt-receiving hole enough tosecurely lock the bolt to the body.
 17. The method of claim 14 includingtightening the screw set pin sufficiently far into the bolt that edgecontact areas of the fingers deform and dig into the tapered end sectionof the pin shaft enough to securely lock the screw set pin to the bolt.18. A method of increasing a mechanical advantage of a self-locking boltassembly including a bolt including a threaded shank having an axialbore extending through the shank for receiving a screw set pin includinga screw section having threads for engaging a threaded bore section ofthe bore, the screw set pin also including a tapered end section, themethod comprising: (a) providing a bore midsection between the threadedbore section and the tapered end section; (b) providing a plurality ofslits in a distal end section of the shank; (c) providing a pin shafthaving one end attached to the screw section and a tapered end sectionfor engaging the tapered end section of the bore, the pin shaft beingsufficiently long to ensure that when the tapered end section of the pinshaft engages the tapered end section of the bore the screw set pin thencan be screwed a predetermined distance further into the bore withoutgalling threads of the screw section and the threaded bore section; and(d) providing an increased distance between proximal ends of the slitsand a contact area at which the tapered end section of the pin shaftengages the tapered end section of the bore by providing the tapered endsection of the pin shaft with a taper angle that is less than a taperangle of the tapered end section of the bore.
 19. A self-locking boltassembly comprising: (a) a bolt including a threaded shank having anaxial bore extending through the shank for receiving a screw set pinincluding a screw section having threads for engaging a threaded boresection of the bore, the screw set pin also including a tapered endsection; (b) a bore midsection between the threaded bore section and thetapered end section; and (c) means for engaging the tapered end sectionof the bore such that when the tapered distal end section engages thetapered end section of the bore the screw set pin then can be tighteneda predetermined distance further into the bore without galling threadsof the screw section and the threaded bore section.
 20. The self-lockingbolt assembly of claim 19 including means for screwing the screw set pinsufficiently far into the bolt to abut the tapered end section of thepin shaft, without galling threads of the shank, and differential tapermeans for causing only a narrowed end portion of the tapered end sectionof the pin shaft to engage a narrowed end portion of the tapered endsection of the bore.
 21. The self-locking bolt assembly of claim 20including differential radius means for locking the self-locking boltassembly into a threaded bolt-receiving hole in a body by tightening thescrew set pin sufficiently far into the bolt to cause the tapered endsection of the pin shaft to sufficiently expand fingers defined by theslits that central contact areas of the fingers elastically deform anddig into the bolt-receiving hole enough to securely lock the bolt to thebody and to cause edge contact areas of the fingers to deform and diginto the tapered end section of the pin shaft enough to securely lockthe screw set pin to the bolt.